Clozapine is an approved and effective drug for treatment of mental illness, but when used in the usual doses causes side effects in many patients. Effective treatment with drugs leads to improvement in symptoms, but often produces other effects which are undesirable, unpleasant, and sometimes disabling. These unwanted effects are known as side effects. The purpose of this research study is to determine whether clozapine at one fifth of the standard dose twice weekly added to a patient's present medication will improve or abolish symptoms (the hoped-for beneficial effect), lead to the appearance of the same side-effects that other patients develop taking the standard higher doses on a daily basis (an undesirable outcome), or a combination of good and bad outcomes. It is also possible that the treatment will have no effect of any kind.